1. Technical Field
The present disclosure is directed to a fluid pressure control device. More particularly, the present disclosure is directed to a system and method for supplying gas at a substantially constant pressure to calibrate a chemical analyzer, such as a blood gas analyzer.
2. Background of Related Art
Chemical analyzers measure a wide range of parameters in various fluids, for example, blood components. In order to calibrate some chemical analyzers, a pressurized fluid canister is provided to supply pressurized gases to the chemical analyzer in incremental measurement cycles. Calibration gases are typically a mixture of Nitrogen (N2), Oxygen (O2), and Carbon dioxide (CO2). One type of chemical analyzer device, available from OPTI Medical Systems, employs a single-use cassette containing elements required for calibration of the chemical analyzer device. As heat is applied to the cassette, a calibration gas mixture is passed across the device sensors.
In many gas calibration systems used in chemical analysis, the pressure of the gas flowing from the pressurized fluid canister is governed by a mechanical pressure regulator. The regulator ensures that gas is supplied to the device within a desired pressure range. Other gas calibration systems employed in chemical analyzers maintain sensor integrity of the analyzer by using refrigerated storage of the sensors themselves, or employ liquid mixing systems to ensure proper operation. However, as can be imagined, the addition of refrigeration systems and/or liquid mixing features increases the complexity of such systems and provides additional sources of error or failure in the use of such systems. Further, gas calibration systems that employ liquid mixing or refrigeration require a steady supply chain of refrigerants, and a demanding maintenance cycle.
One concern associated with current systems to calibrate, for example, a blood gas analyzer, surrounds the relative high pressure of the canister of fluid. Canisters of fluid pressurized in excess of 30 psi are typically classified as hazardous goods for air transportation purposes, and thus are subject to high shipping costs. Similarly, canisters of fluid pressurized in excess of 60 psi are often categorized as hazardous goods for ground transportation. Thus, for many current canisters of fluid, the associated shipping costs can approach or even exceed the cost of the canister of fluid to the consumer.
Another concern associated with the mechanical pressure regulators currently in use is that they incur high costs relative to other components of the fluid pressure control device and chemical analyzer. Often this one component is the single most expensive component of the fluid pressure control device and the chemical analyzer.
Yet a further drawback of mechanical pressure regulators is that they require periodic purging because of CO2 diffusion through the various seals and diaphragms of the mechanical pressure regulator. This problem is compounded over longer periods of operation. Thus, because of the periodic purging, a significant portion of the gas stored in the canister of fluid is simply wasted to ensure that the calibration gas used in calibration is comprised of the appropriate proportions of CO2 and other gases. Moreover, in order to function properly mechanical pressure regulators require a minimum pressure in the pressurized fluid canister. Once the pressure in the canister drops below the threshold pressure, typically about 25 psi, the remaining volume of gas in the canister of fluid is simply wasted.
Accordingly, it is desirable to provide a fluid pressure control device to supply calibration gases to a chemical analyzer that employs a relatively low-pressure canister of fluid and avoids the need for a mechanical pressure regulator, thereby avoiding the waste, high costs, and maintenance associated with current systems.